This indicates an attack attempt against a Cross-Site Scripting (XSS) vulnerability in Artica Web Proxy.
The vulnerability,which is caused by a lack of sanitizing of the parameter "username-form-id" that is passed to "freeradius.users.php".A remote attacker can exploit this to execute arbitrary script code within the context of the user's browser.
Artica Web Proxy before 3.06.112911
System Compromise: Remote attackers can execute arbitrary script code within the context of the target user's browser.
Upgrade to the latest version, available from the web site.